Myeloid leukaemia and malignant lymphoma in mice after X-ray and neutron exposure

Purpose: To determine neutron RBE for myeloid leukemia and malignant lymphoma.

Status: 1980 - 1984, terminated

Treatment: Single exposure to 250 kVp X-rays (133 mGy/min, 1.5 mm HVL) or fission neutrons (4 mGy/min, 0.4 MeV) from the biological facility of the RSV-TAPIRO reactor at Casaccia.

Dosimetry: Twin ionization chamber method, ENDIP

Endpoints: Life-span study (spontaneous death) with macroscopic/microscopic pathology

Animal: Male (C57Bl/Cne x C3H/Cne)F1 (BC3F1) mice aged 3 months

Results: The data on the induction of lymphoma and myeloid leukemia yielded some new interesting shapes of dose-effect relationships which were interpreted by radiobiological models of the process of induction in conjunction with cell inactivation. The dose-effect relationship for malignant lymphoma induced by X-rays can be described by a quadratic model corrected for cell inactivation whereas that for neutrons is best fitted to a linear model with also allows for cell inactivation. Myeloid leukemia yielded a bell-shaped curve after irradiation with X-rays or neutrons which can be explained by simultaneous mechanisms of cell transformation and cell inactivation.. The data on cell inactivation at higher doses agree with those reported in other mouse strains. A relative biological efficiency of 4 was found for neutrons at the lowest neutron dose used. The value of the inactivation parameters can be compared with those of the cell inactivation probability per unit dose for bone marrow hemopoietic stem cells which are considered to be the target cells for these tumors.